Reciprocating combustion engines are known for converting chemical energy from a fuel source into rotating shaft power. In reciprocating engines, air is compressed within a cylinder volume defined by a piston, an inner cylinder wall, and a cylinder head, thereby increasing both the pressure and temperature of the air. In spark ignition engines, fuel and air are premixed upstream of the cylinder volume or within the cylinder volume, such that ignition of the premixed fuel and air is initiated by arcing an electrical spark across a gap within the cylinder volume. In compression ignition engines, a fuel-air mixture within the cylinder volume autoignites in response to the local temperature and pressure within the volume. More particularly, in direct injection compression ignition engines, fuel is injected into the cylinder volume near the peak of the compression cycle and ignition of the fuel and air occurs after a short autoignition delay time. Heat released from combustion of the fuel-air mixture does work against the piston, which conventionally transfers the work to a rotating crankshaft through a connecting rod.
Canadian patent number 2743043 (hereinafter “the '043 patent”) describes a dual fuel injection valve for direct injection of two different fuels into a combustion chamber of an internal combustion engine. The '043 patent states that a first fuel can be selected from a group of combustible gases including natural gas, hydrogen, and propane, and that a second pilot fuel can be selected from a group of combustible liquids including diesel fuel, dimethylether, and bio-diesel.
The '043 patent describes high pressure direct injection (HPDI) of the first fuel near top dead center of a piston compression stroke. In turn, the supply pressure of the first fuel must be in excess of the cylinder pressure at the time of injection to effect direct injection of the first fuel. However, on-vehicle storage of fuels at such high pressures or on-vehicle compression of gaseous fuels to such high pressures is difficult and expensive.
Further, injecting the first (gaseous) fuel near the top of the compression stroke, as described in the '043 patent, may not allow sufficient time for mixing with air inside the cylinder, which can be problematic for ignition. For example, injecting the second fuel into a region of largely unmixed first fuel could inhibit ignition by shielding the second fuel from oxygen. Moreover, ignition of the second fuel may not effect ignition of the first fuel if the first injection and the second injection are separated by a region of air largely devoid of either fuel.
Accordingly, apparatus and methods for injecting gaseous fuel into a compression ignition engine with improved fuel-air mixing and with reduced storage and delivery pressure requirements are desired.